The present invention relates, in general, to body structures in the automobile industry, and more particularly to an open-profile, elongate structural body part as safety elements for automobile body construction.
Structural body parts in the form of thin-walled side impact supports, bumpers, cross members, longitudinal member, roof frames and column reinforcements are known. Because of more stringent requirements, the use of high strength and highest strength steels has increased. The structural body parts, in general, are manufactured as pressed parts from sheet steel. In addition to a very high strength, such structural body parts must have a minimum ductility of 5% to 10%.
The use of cold-formable, high strength steels has also been proposed. However, these steels are suitable only for structural body parts with a simple shaping because of their limited shaping and deforming properties. Another approach involves the use of hardenable steel sheets. These steel sheets in the form of blanks or coil material are shaped in pressing tools to structural body parts while still soft. The structural body parts are then provided with the required strength in a subsequent hardening process. These steel sheets in their soft state have sufficient shaping and deforming properties and thus can be used to produce structural body parts of complex shape. One example of a material with such properties includes 22 Mn B5 mod. This material has in its soft state a strength of approximately 600 N/mm2 and a ductility of greater than 30%. After hardening, strength values of up to 1600 N/mm2 with 10% ductility can be achieved.
Heating to the austenitizing temperature for the purpose of hardening is frequently performed heretofore by gas-heated or electrically heated continuous furnaces. In order to ensure a continuous production, such continuous furnaces are integrated into the manufacturing line for the structural body parts. However, a disadvantage is the great space requirement of such continuous furnaces. Furthermore, it should be noted that energy consumption is considerable and that heat losses cannot be avoided. Also, when using continuous furnaces, it is not possible to perform a partial or regional hardening of the structural body parts.
It is also known to shape hardenable steel sheets to the desired structural body parts with combination shaping and hardening tools. In this case, the blanks are heated before shaping to the austenitizing temperature and are then simultaneously shaped and hardened in a cooled shaping tool. This process also necessarily entails high tool and energy technological expenditures. Furthermore, this process increases considerably increases the cycle times during the shaping step.
It is also known to use inductive hardening for massive steel products, such as crankshafts, gears, bearing etc., as well as for closed elongate sections.
It would therefore be desirable and advantageous to provide an improved apparatus for heat treatment of open-profile elongate structural body parts in the automobile industry from ultrahigh-strength pressing parts so as to meet safety functions while requiring only minimal manufacturing and tool expenditure and ensuring a high efficiency with reduced energy consumption.